X-ray study of the hetero ring flexibility in saturated and partially saturated 3,1-benzoxazin-2-ones and 3,1-benzoxazine-2-thiones [1]: The structures of cis-4a,5,8,8a-tetrahydro-4 H-3,1-benzoxazin-2(1 H)-one, cis-4a,5,8,8a-tetrahydro-4 H-3,1-benzoxazine-2(1 H)-thione and cis-4a,5,6,7,8,8a-hexahydro-4 H-3,1-benzoxazine-2(1 H)-thione

Abstract

The structures of the title compounds have been established by X-ray crystallography from diffractometer data. The crystals of the first (I), C 8H 11 NO 2, are monoclinic space group P2 1/ n, with a = 11.266(2), b = 9.638(1), c = 7.500(1) Å, β = 109.16(1)°, Z = 4, D c = 1.323 g cm −3. The crystals of the second (II), C 8H 11NOS, are also monoclinic, space group P2,/ n, with c = 7.681(1), b = 10.007(1), c = 11.207(1) Å, β = 106.06(1)°, Z = 4, D c = 1.358 g cm −3. The crystals of the third (III), C 8H 12NOS, are orthorhombic, space group Pbca, with a = 11.862(8), b = 15.751(8), c = 18.375(8) Å, Z = 16, D c = 1.325 g cm −3. The structures determined by direct methods have been refined to R = 0.037 for 1343 reflections of I, R = 0.038 for 1605 reflections of II, and R = 0.042 for 2595 of III. The conformations of the hetero rings have been compaired with the related 1-methyl- cis-4a,5,6,7,8,8a-hexahydro-4 H-3,1-benzoxazine-2(1 H)-thione (IV) [2]. The flexibility of the 2-oxo- and 2-thioxo derivatives of the 1,3-oxazine ring fused with different carbocycles is rather limited. The ring invariably assumes a conformation close to envelope 1 E slightly distorted towards half-chair 3 H 6, which may be attributed to the intrinsic properties of these rings (e.g. the rather short endo C(2)O bond, etc.).